1. Field of Invention
The present invention relates to a front axle of an agricultural tractor.
2. Background of Prior Art
The present invention relates to a hitch device for attaching farm implements to a tractor.
More specifically, the present invention relates to a so-called “three-point hitch device”, to which the following description refers purely by way of example.
In the farm machinery industry, a three-point hitch device is known for attaching farm implements to a tractor, and which normally comprises two bottom lift arms, to which the implement is connected in rotary manner to oscillate about a given hinge axis; and a top actuating cylinder interposed between the tractor frame and the implement to control the angular position of the implement about the hinge axis.
Each lift arm is moved by a further actuating cylinder interposed between the tractor frame and the lift arm itself, and having an output rod defining, inside the further actuating cylinder, two chambers, each of which is connected to a feed line of a hydraulic circuit supplying pressurized fluid to and from the chambers.
The hydraulic circuit comprises a slide valve located along the feed lines and movable selectively between a closed position and three open positions closing and opening the feed lines respectively. In two of the open positions, one of the two feed lines communicates hydraulically with a pump supplying fluid to the relative chamber, and the other communicates hydraulically with a fluid tank; and, in the third open position, both feed lines communicate hydraulically with the tank.
The hydraulic circuit also comprises a lock valve interposed between the feed lines and relative chambers to keep the output rod in a given position when the slide valve is in the closed position.
A major drawback of known hitch devices of the above type is that, when the slide valve is moved to the third open position, the lock valve must be operated to connect both chambers hydraulically to the tank. Moreover, operation of the lock valve is relatively complex and not very precise.
It is an object of the present invention to provide a hitch device for attaching farm implements to a tractor, designed to eliminate the aforementioned drawbacks.